1. Field of the Invention
The present invention relates to a liquid-crystal projection device i.e. what is known as a projector and in particular relates to improvements in the light source and peripheral optical system of a small-size liquid-crystal projection device.
2. Description of the Related Art
As the light sources employed is conventional liquid-crystal projection devices, light sources using a fluorescent tube or light-guide plate or electrical discharge-type light sources such as metal halide lamps have come to be employed.
In particular, Japanese Patent Laid-Open number Sho. 51-119243 discloses a flat plate-shaped light source. This specification states that the flat plate-shaped light source employs electroluminescence i.e. electroluminescent elements.
However, in the case of a light source employing a fluorescent tube or light-guide plate, it is difficult to make the diameter of the fluorescent tube etc. small. There was therefore the problem that miniaturization of a liquid-crystal projection device was difficult, since the thickness of the light source itself could not be reduced below the diameter of the fluorescent tube.
Also, in the case of an electric discharge-type light source such as a metal halide lamp, the reflector of large aperture that was considered necessary to direct the light diverging from the light source parallel to the liquid crystal panel was a factor impeding miniaturization of the liquid-crystal projection device.
In particular in the case of a liquid-crystal projection device for color display, further miniaturization the liquid-crystal projection device was difficult owing to the need to provide liquid crystal display elements consisting of a light source as aforementioned and liquid crystal panel for each of the primary colors constituting the color image.
Also, Japanese Patent Laid-Open number Sho. 51-119243 does not clearly disclose a material constituting a luminescent layer of an electroluminescent element. When the conventional inorganic electroluminescent material is employed as material for this luminescent layer, light from the electroluminescent element is light of a highly divergent character. This therefore suffered from the problem that projection of a bright image could not be achieved since the light could not be effectively directed into the aperture of the projection lens.
A further problem was that the drive voltage required for an electroluminescent element using inorganic material is at least 100 volts, which is comparatively high.
An object of the present invention is to provide a liquid-crystal projection device wherein, in order to solve the above problems, greater miniaturization than conventionally can be achieved and in which a bright image can be projected with low voltage.
In more detail, a first task of the present invention is to provide a miniature liquid-crystal projection device that can be driven with lower voltage than conventionally and in which a brighter image than conventionally is projected by preventing the diminution in the amount of light produced by divergence of the light, by employing an organic electroluminescent element having a resonator structure where light of good optical emission directionality is emitted.
A second task of the present invention is to provide a miniature liquid-crystal projection device in which a brighter image than conventionally is projected by increasing the amount of light that can be transmitted through a polarizing plate of the liquid crystal panel by using a polarization conversion element that can convert a polarization of the emitted light from the light source.
A third task of the present invention is to provide a miniature liquid-crystal projection device in which a brighter image than conventionally is projected, by increasing the amount of light that is transmitted through the polarizing plate of the liquid crystal panel by employing a polarization conversion element that functions in a specified wavelength band in projecting a color image.
A fourth task of the present invention is to provide a miniature liquid-crystal projection device in which a brighter image than conventionally is projected by increasing the amount of light that is transmitted through the aperture of a pixel and miniaturizing the device itself by employing a miniature luminescent element comprising a microlens array element that focuses the light on to pixel apertures of the liquid crystal panel.
A fifth task of the present invention is to provide a miniature liquid-crystal projection device in which a clear image is projected by raising the purity of the light that is projected and the brightness compared with conventional devices, by increasing the amount of light consisting of light of only a specified wavelength by employing miniature luminescent elements that emit light of only a specified wavelength, due to optical resonance, in projection of a color image.
A liquid-crystal projection device includes a liquid crystal display element. The liquid crystal element includes an organic electroluminescent element constructed by sandwiching an organic thin-film element between an electrode layer that reflects light and an electrode layer that transmits lights; and a transparent liquid crystal panel that controls the transmission of light emitted from a face of the organic electroluminescent element.
The liquid-crystal projection device may include an organic thin-film layer formed from as a white luminescent layer that emits white light.
The organic thin-film layer may be formed by successively stacking primary color luminescent layers that respectively emit light of respective wavelength regions of a plurality of primary colors necessary for color display.
The organic electroluminescent may be formed of a transparent electrode layer overlying a transparent substrate, the organic thin-film layer overlying the transparent electrode layer and an electrode layer overlying the organic thin-film layer and that reflects light emitted by the organic thin-film layer.
The organic electroluminescent element may include an electrode layer that reflects light emitted from the organic thin-film layer; a transparent electrode layer that sandwiches the organic thin-film layer between itself and the electrode layer; and a half-mirror layer provided on the optical output side from the transparent electrode layer and that reflects some of the incoming light through the transparent electrode layer into the electrode layer, while transmitting the rest of the light; and the distance between the half-mirror layer and the electrode layer is set to an optical distance that produces resonance of the light.
Between the organic electroluminescent element and the transparent liquid crystal panel there maybe further provided a polarization conversion element that converts the polarization condition of emitted light from the organic electroluminescent element, and the transparent liquid crystal panel maybe provided with a polarizing plate that transmits light of a specified polarization, of the light emitted alter passing through the polarization conversion element.
The polarization conversion element may include a circular polarization selective reflection filter arranged on the organic electroluminescent element side and that reflects one circularly polarized component of right-handed circularly polarized light and left-handed circularly polarized light and that transmits the other circularly polarized component, and a xc2xc wavelength plate that converts circularly polarized light to linearly polarized light and that converts linearly polarized light to circularly polarized light.
The polarization conversion element may include a linearly polarized light selective reflection filter arranged on the transparent liquid crystal panel side and that, of two perpendicular linearly polarized components, reflects one linearly polarized component and transmits the other linearly polarized component, and a xc2xc wavelength plate that converts circularly polarized light into linearly polarized light and that converts linearly polarized light into circularly polarized light.
The polarization conversion element may include a polarization selective reflection filter that, for the emitted light of a specified wavelength region, transmits light of a specified polarization and reflects light of other polarizations.
Between the organic electroluminescent element and the transparent liquid crystal panel, there may further be provided a front-side microlens array element wherein microlens elements that collect output light from the organic electroluminescent element are arranged corresponding to individual pixels of the transparent liquid crystal panel.
A focal length of the microlens elements and the distance between the front-side microlens array element and this liquid crystal panel are adjusted such that the apertures of the individual pixels of the transparent liquid crystal panel are arranged in the vicinity of the rear-side focal point of the microlens elements.
The transparent liquid crystal panel may include an optical screening element that transmits light that is incident on the aperture of each pixel and that screens light that is incident on portions other than the aperture of this pixel. The liquid-crystal projection device may further include a rear-side microlens array element constituted by arranging, corresponding to individual pixels, microlens elements that suppress divergence of light transmitted through the pixel apertures of the liquid crystal panel, on the side where light is output after passing through the transparent liquid crystal panel.
A focal length of the microlens elements and the distance between the rear-side microlens array element and the transparent liquid crystal panel are adjusted such that the apertures of the pixels are arranged in the vicinity of the front-side focal point of the rear-side microlens elements.
Between the organic electroluminescent element and the front-side microlens array element, there may be further provided a polarization conversion element that converts the polarization of light that is output from the organic electroluminescent element, and the transparent liquid crystal panel may include a polarizing plate that transmits light of a specified polarization, of the light that is output after passing through the polarization conversion element.
The polarization conversion element may include a circular polarization selective reflection filter arranged on the organic electroluminescent element side and that reflects one circularly polarized component of right-handed circularly polarized light and left-handed circularly polarized light and that transmits the other circularly polarized component, and a xc2xc wavelength plate that converts circularly polarized light into linearly polarized light and that converts linearly polarized light into circularly polarized light.
The polarization conversion element may include a linear polarization selective reflection filter arranged on the front-side microlens array element side and that, of two perpendicular linear polarization components, reflects one linearly polarized component and transmits the other linearly polarized component, and a xc2xc wavelength plate that converts circularly polarized light into linearly polarized light and that converts linearly polarized light into circularly polarized light.
A liquid-crystal projection device may be further provided with a projection lens that projects on to a screen an image generated by passing through the transparent liquid crystal panel.
The liquid-crystal projection device may be further provided with a transparent screen whereby an image projected from the projection lens can be observed from the opposite side of this projection lens.
The liquid-crystal projection device may be further provided with a plurality of liquid crystal display elements that control the transmission of light of respective wavelength regions of a plurality of primary colors necessary for color display; a combining optical system that generates a color image by combining images of primary colors emitted from the plurality of liquid crystal display elements; and a projection lens that projects on to a screen a color image combined by the combining optical system.
The plurality of organic electroluminescent elements may be provided with an optical resonant structure.
The liquid-crystal projection device may include for each primary color, liquid crystal display elements including organic electroluminescent elements having an optical resonant structure adjusted such as to emit light of respective wavelength regions of a plurality of primary colors necessary for color display and a transparent liquid crystal panel that controls the transmission of light emitted from the face of the organic electroluminescent elements; and further comprising a combining optical system that generates a color image by combining images of each primary color emitted from the respective liquid crystal display elements, and a projection lens that projects on to a screen the color image combined by the combining optical system.
The liquid-crystal projection device may also include a transparent screen constituted so that an image projected from the projection lens can be observed from the opposite side of the projection lens.
The liquid crystal display elements may further include, between the organic electroluminescent element and the transparent liquid crystal panel, a front-side microlens array constituted by arranging, corresponding to individual pixels of the transparent liquid crystal panel, microlens elements that collect the light emitted from the organic electroluminescent element.
The liquid crystal display elements may further include a rear-side microlens array element constituted by arranging, corresponding to each pixel, microlens elements that suppress divergence of light passing through the pixel apertures of the liquid crystal panel, on the output side of light that has passed through the transparent liquid crystal panel.
The front-side microlens array element and the rear-side microlens array element of the liquid crystal display elements may include a reflection preventing film adjusted such that its reflectivity is lowest for light of the wavelength region of the primary color allocated to the liquid crystal display element.
The liquid crystal display elements, between the organic electroluminescent element and the front-side microlens array element, may be further provided with a polarization conversion element that converts the polarization of emitted light, from the organic electroluminescent element, and the transparent liquid crystal panel may be provided with a polarizing plate that transmits light of a specified polarization condition of light that is emitted after having passed through the polarization conversion element.
The polarization conversion element of the liquid crystal display elements may include a polarization selective reflection filter that transmits light of specified polarization with respect to the emitted light of a specified wavelength region and that reflects light of other polarizations.